The present disclosure relates to a control device for a voltage source converter and an operating method thereof, and more particularly, to a control device for a voltage source converter associated with a wind farm and an operating method thereof.
In general, a high voltage direct current (HVDC) is associated with an HVDC transmission method in which alternating current (AC) power generated in a power station is converted into DC power, the DC power is transmitted and then re-converted into the AC power in a power receiving region.
Since the HVDC is high in power transmission efficiency and low in power loss, all the countries of the world are widely utilizing it from high voltage power transmission to distribution.
In recent, wind power and solar light are recognized as essential technologies for the reduction of a greenhouse gas and expansion in the distribution of new renewable energy and thus an interest in the HVDC is increasing.
Also, the HVDC is being recognized as a core technology in the power industry field of a country due to a high ripple effect throughout related fields such as semiconductor power electronics, computer, control, communication, electricity, machine design, and analysis engineering.
Such an HVDC system is classified into a current type HVDC system using a thyristor valve and a voltage source converter (VSC) based HVDC system using an insulated gate bipolar mode transistor (IGBT) element.
Since the VSC based HVDC may supply active power and reactive power, it is also suitable for small isolated grid connection having no separate power supply, and since the VSC based HVDC has a smaller conversion station in comparison to the current type HVDC and may implement a black start function, it is suitable for marine platform having no AC power supply.
Due to the advantages of the VSC based HVDC, a plan and project for connecting a remote, new renewable energy farm by using the VSC based HVDC are increasing.
When in a general multi-terminal DC transmission device, an AC grid and a wind farm are together connected, they are controlled by a remote control 500.
Related descriptions are provided with reference to FIG. 1.
FIG. 1 is a schematic diagram of a general multi-terminal DC transmission device.
The multi-terminal DC transmission device in FIG. 1 is a system having four terminals, each being connected to an AC grid connected to a transformer 400 or a wind farm 300.
In addition, there are line impedance R+jwL and grid impedance between a voltage source converter 200 and the AC grid.
Each terminal includes the voltage source converter 200 and is controlled by the remote control 500.
Since the remote control 500 is spaced apart from each voltage source converter 200, it may control each voltage source converter 200 through communication.
When the remote control 500 connected to each voltage source converter 200 experiences communication failure, the remote control 500 may not control each voltage source converter 200 and one or more voltage source converters 200 does not normally operate, each voltage source converter 200 is in a backup operation mode.
Thus, each voltage source converter 200 operates a backup controller such as a droop controller so that the power transmission of a whole DC transmission system is consistently performed.
However, when the voltage source converter 200 may not communicate with the wind farm 300, the power transmission control from the voltage source converter 200 connected to the wind farm may not normally operate.
The reason for this is because the control of a general wind power generator is performed by a using maximum power point tracking (MPPT) technique, a whole DC transmission device experiences an excessive power supply, the common DC bus voltage of the multi-terminal DC transmission device rises and thus there is a limitation in that the continuous operation of a DC transmission device becomes difficult.